JP2021097036A - Coated positive electrode active material for lithium ion battery and manufacturing method thereof - Google Patents

Abstract

To provide a coated positive electrode active material for a lithium ion battery capable of obtaining a lithium ion battery having excellent cycle characteristics.SOLUTION: In a coated positive electrode active material (P) for a lithium ion battery formed by coating at least a part of the surface of a positive electrode active material for a lithium ion battery with a coating layer including a polymer compound for coating and a conductive agent, the coverage measured by X-ray photoelectron spectroscopy is 65 to 96%.SELECTED DRAWING: None

Description

The present invention relates to a coated positive electrode active material for a lithium ion battery and a method for producing the same.

In recent years, there has been an urgent need to reduce carbon dioxide emissions for environmental protection. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions by introducing electric vehicles (EVs) and hybrid electric vehicles (HEVs), and the development of secondary batteries for driving motors, which holds the key to their practical application, is enthusiastic. It is done. As a secondary battery, a lithium ion secondary battery that can achieve a high energy density and a high output density is attracting attention, and an electrolytic solution and an active material are being improved in order to further improve the performance.

Among them, as a positive electrode active material that enables the production of batteries with high energy density by suppressing the irreversible reaction between the electrolytic solution and the active material, a composite positive electrode active material having a specific amount of polymer on the surface of the active material has been proposed. (See Patent Document 1).

Japanese Unexamined Patent Publication No. 2001-202954

However, the non-aqueous electrolyte secondary battery using the composite positive electrode active material described in Patent Document 1 has a problem in the charge / discharge characteristics of the lithium ion battery, for example, sufficient cycle characteristics may not be obtained.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a coated positive electrode active material for a lithium ion battery capable of obtaining a lithium ion battery having excellent cycle characteristics.

The present inventors have arrived at the present invention as a result of studies for achieving the above object. That is, the present invention is a coated positive electrode active material for a lithium ion battery, wherein at least a part of the surface of the positive electrode active material for a lithium ion battery is coated with a coating layer containing a coating polymer compound and a conductive agent. The coated positive electrode active material (P) for a lithium ion battery having a coverage of 65 to 96% as measured by X-ray photoelectron spectroscopy; the method for producing a coated positive electrode active material for a lithium ion battery, wherein the lithium ion is used. It has a step of mixing a positive electrode active material for a battery, a polymer compound for coating, a conductive agent, and a solvent, and the difference between the surface free energy of the positive electrode active material for a lithium ion battery and the surface free energy of the solvent. This is a method for producing a coated positive electrode active material for a lithium ion battery, wherein the absolute value (ΔE) of is 10 to 30 mN / m.

By using the coated positive electrode active material (P) for a lithium ion battery of the present invention, a lithium ion battery having excellent cycle characteristics can be obtained.

<Positive electrode active material for lithium-ion batteries>
As the positive electrode active material for a lithium ion battery constituting the coated positive electrode active material (P) for a lithium ion battery of the present invention, a conventionally known positive electrode active material can be preferably used, and lithium ions are inserted by applying a certain potential. A compound capable of inserting and removing lithium ions at a higher potential than the negative electrode active material for a lithium ion battery used for the counter electrode can be used.

The cathode active material for a lithium ion battery, a composite oxide composite oxide of lithium and transition metal {transition metal is one (e.g. _{LiCoO 2, LiNiO 2, LiAlMnO 4} , LiMnO 2 and LiMn ₂ O _4), composite oxide transition metal element is two (e.g. _{LiFeMnO 4, LiNi 1-x Co} x O 2, LiMn 1-y Co y O 2, LiNi 1/3 Co 1/3 Al 1/3 O 2, LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _0.77 Co _0.2 Al _0.03 O _2, LiNi _0.83 Co _0.14 Al _0.03 O ₂ and LiNi _0.87 Co _{0 .08} Al _0.05 O ₂ ), a composite oxide containing three or more transition metal elements [for example, LiA _a B _b C _c ... N _n O ₂ (A, B, C and N are different metal elements). For example, LiNi _1/3 Co _1/3 Mn _1/3 O _2, LiNi _0.9 Co _0.04 Al _0.02 Mn _0.04 O ₂ and LiNi _{0. .86} Co _0.06 Al _0.02 Mn _0.06 O ₂ )]}, lithium-containing transition metal phosphates (eg LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ and LiNiPO ₄ ), transition metal oxides (eg MnO _2). And V ₂ O ₅ ), transition metal sulfides (eg MoS ₂ and TiS ₂ ) and conductive polymers (eg polyaniline, polypyrrole, polythiophene, polyacetylene and poly-p-phenylene and polyvinylcarbazole), etc. The above may be used together.
The lithium-containing transition metal phosphate may be one in which a part of the transition metal site is replaced with another transition metal.

The volume average particle size of the positive electrode active material for a lithium ion battery is preferably 0.01 to 100 μm, more preferably 0.1 to 35 μm, and 2 to 30 μm from the viewpoint of the electrical characteristics of the battery. Is even more preferable.

In the present specification, the volume average particle size of the positive electrode active material for a lithium ion battery means the particle size (Dv50) at an integrated value of 50% in the particle size distribution obtained by the microtrack method (laser diffraction / scattering method). The microtrack method is a method for obtaining a particle size distribution using scattered light obtained by irradiating particles with laser light. A microtrack or the like manufactured by Nikkiso Co., Ltd. can be used for measuring the volume average particle size.

<Polymer compound for coating>
The coating polymer compound [hereinafter, may be abbreviated as a polymer compound] constituting the coating layer is an ester compound of a monovalent aliphatic alcohol having 1 to 12 carbon atoms and (meth) acrylic acid, which will be described later. It is preferably a polymer of a monomer composition containing a11) and an anionic monomer (a12).
In addition, in this specification, (meth) acrylic acid means methacrylic acid or acrylic acid.

The acid value (unit: mgKOH / g) of the polymer compound in the present invention is preferably 5 to 200, more preferably 7 to 100, and particularly preferably 10 to 50 from the viewpoint of the cycle characteristics of the lithium ion battery described later. is there.
The acid value can be appropriately adjusted depending on the type and weight ratio of each monomer constituting the polymer compound. For example, when the weight of the ester compound (a11) is large among all the monomers constituting the polymer compound, the acid value is small.
The acid value is measured by the method of JIS K 0070-1992.

<Ester compound (a11)>
The ester compound (a11) in the present invention is an ester compound of a monohydric aliphatic alcohol having 1 to 12 carbon atoms and (meth) acrylic acid. Examples of the monohydric aliphatic alcohol having 1 to 12 carbon atoms include monohydric branched or linear aliphatic alcohols having 1 to 12 carbon atoms, and methanol, ethanol, propanol (n-propanol, iso-propanol), and the like. Butyl alcohol (n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol), pentyl alcohol (n-pentyl alcohol, 2-pentyl alcohol, neopentyl alcohol, etc.), hexyl alcohol (1-hexanol, 2-hexanol and 3) -Hexanol, etc.), heptyl alcohol (n-heptyl alcohol, 1-methylhexyl alcohol, 2-methylhexyl alcohol, etc.), octyl alcohol (n-octyl alcohol, 1-methylheptanol, 1-ethylhexanol, 2-methylhepta, etc.) Nord and 2-ethylhexanol, etc.), nonyl alcohol (n-nonyl alcohol, 1-methyloctanol, 1-ethylheptanol, 1-propylhexanol, 2-ethylheptyl alcohol, etc.), decyl alcohol (n-decyl alcohol, 1) -Methylnonyl alcohol, 2-methylnonyl alcohol, 2-ethyloctyl alcohol, etc.), undecyl alcohol (n-undecyl alcohol, 1-methyldecyl alcohol, 2-methyldecyl alcohol, 2-ethylnonyl alcohol, etc.), lauryl Examples thereof include alcohols (n-lauryl alcohol, 1-methylundecyl alcohol, 2-methylundecyl alcohol, 2-ethyldecyl alcohol, 2-butylhexyl alcohol, etc.).

Among the above ester compounds (a11), from the viewpoint of cycle characteristics, preferred are methyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-methylhexyl (meth) acrylate, ( 2-Ethylhexyl acrylate, dodecyl (meth) acrylate and their combined use, more preferably 2-ethylhexyl methacrylate and dodecyl methacrylate, still more preferably dodecyl methacrylate. Based on the weight of the ester compound (a11), it is particularly preferable that the dodecyl methacrylate is 30% by weight or more (more preferably 60% by weight or more).

<Anionic monomer (a12)>
The anionic monomer (a12) is a monomer having a polymerizable group having a radical polymerizable property and an anionic group. Preferred examples of the radically polymerizable group include a vinyl group, an allyl group, a styrenyl group and a (meth) acryloyl group, and preferred anionic groups include a phosphonic acid group, a sulfonic acid group and a carboxyl group. Can be mentioned.

Preferred anionic monomer (a12) is a radically polymerizable unsaturated carboxylic acid having 3 to 9 carbon atoms, a radically polymerizable unsaturated sulfonic acid having 2 to 8 carbon atoms, and a radical polymerization having 2 to 9 carbon atoms. There is at least one selected from the group consisting of sex unsaturated phosphonic acids.

Examples of the radically polymerizable unsaturated carboxylic acid having 3 to 9 carbon atoms include a radically polymerizable unsaturated aliphatic monocarboxylic acid having 3 to 9 carbon atoms and a radically polymerizable unsaturated aromatic monocarboxylic acid having 9 carbon atoms. ..
Examples of the radically polymerizable unsaturated aliphatic monocarboxylic acid having 3 to 9 carbon atoms include (meth) acrylic acid, butanoic acid (including substituted butanoic acid such as 2-methylbutanoic acid and 3-methylbutanoic acid), and pentenic acid (2). -Contains substituted pentenoic acid such as methylpentanoic acid and 3-methylpentenoic acid), hexenoic acid (including substituted hexenoic acid such as 2-methylhexenoic acid and 3-methylhexenoic acid), heptenoic acid (2-methylheptenoic acid). Examples thereof include acids and substituted heptenic acids such as 3-methylheptanoic acid) and octenoic acid (including substituted octenoic acids such as 2-methyloctenoic acid and 3-methyloctenoic acid).
Examples of the radically polymerizable unsaturated aromatic monocarboxylic acid having 9 carbon atoms include 3-phenylpropene acid and vinyl benzoic acid.

Examples of the radically polymerizable unsaturated sulfonic acid having 2 to 8 carbon atoms include a radically polymerizable unsaturated aliphatic monosulfonic acid having 2 to 8 carbon atoms and a radically polymerizable unsaturated aromatic monosulfonic acid having 8 carbon atoms. ..
Examples of the radically polymerizable unsaturated aliphatic monosulfonic acid having 2 to 8 carbon atoms include vinyl sulfonic acid (including substituted vinyl sulfonic acid such as 1-methyl vinyl sulfonic acid and 2-methyl vinyl sulfonic acid) and allyl sulfonic acid (including substituted vinyl sulfonic acid such as 1-methyl vinyl sulfonic acid and 2-methyl vinyl sulfonic acid). Includes substituted allyl sulfonic acid such as 1-methylallyl sulfonic acid and 2-methylallyl sulfonic acid), butene sulfonic acid (including substituted butene sulfonic acid such as 1-methyl butene sulfonic acid and 2-methyl butene sulfonic acid). ), Penten sulfonic acid (including substituted penten sulfonic acid such as 1-methylpenten sulfonic acid and 2-methyl penten sulfonic acid) Hexen sulfonic acid (substituted hexene such as 1-methyl hexene sulfonic acid and 2-methyl hexene sulfonic acid) Includes sulfonic acid) and heptene sulfonic acid (including substituted heptene sulfonic acid such as 1-methyl heptene sulfonic acid and 2-methyl heptene sulfonic acid) and the like.
Examples of the radically polymerizable unsaturated aromatic monosulfonic acid having 8 carbon atoms include styrene sulfonic acid.

Examples of the radically polymerizable unsaturated phosphonic acid having 2 to 9 carbon atoms include vinylphosphonic acid, allylphosphonic acid, vinylbenzylphosphonic acid, 1- or 2-phenylethenylphosphonic acid, (meth) acrylamidealkylphosphonic acid, and acrylamidealkyl. Examples thereof include diphosphonic acid, phosphonomethylated vinylamine and (meth) acrylic phosphonic acid.

One of these anionic monomers (a12) may be used alone, or two or more thereof may be used in combination.
Among the anionic monomers (a12), a radically polymerizable unsaturated carboxylic acid having 3 to 9 carbon atoms is preferable, and (meth) acrylic acid is more preferable from the viewpoint of cycle characteristics. Based on the weight of the anionic monomer (a12), it is particularly preferable that the (meth) acrylic acid is 50% by weight or more (more preferably 70% by weight or more).

The content of the ester compound (a11) contained in the monomer composition is based on the total weight of the ester compound (a11) and the anionic monomer (a12) from the viewpoint of adhesion to the active material and the like. It is preferably 70 to 99% by weight, more preferably 80 to 98% by weight, and particularly preferably 90 to 97% by weight.

The content of the anionic monomer (a12) contained in the monomer composition is preferably based on the total weight of the ester compound (a11) and the anionic monomer (a12) from the viewpoint of ionic conductivity. Is 1 to 30% by weight, more preferably 2 to 20% by weight, and particularly preferably 3 to 10% by weight.

<Salt of anionic monomer (a13)>
The monomer composition of the coating polymer compound may further contain a salt (a13) of an anionic monomer.
It is preferable to contain the anionic monomer salt (a13) because the internal resistance can be reduced and the cycle characteristics can be improved.

Examples of the anion of the anionic monomer constituting the salt (a13) of the anionic monomer include anions of the same anionic monomer as those exemplified in the above-mentioned anionic monomer (a12). At least one anion selected from the group consisting of vinyl sulfonic acid anion, allyl sulfonic acid anion, styrene sulfonic acid anion and (meth) acrylic acid anion is preferable.
Examples of the cation constituting the salt (a13) of the anionic monomer include monovalent inorganic cations, preferably alkali metal cations and ammonium ions, more preferably lithium ions, sodium ions, potassium ions and ammonium ions. Lithium ions are more preferred.
The salt (a13) of the anionic monomer may be used alone or in combination of two or more. When the salt of the anionic monomer (a13) has a plurality of anions, the cations are lithium ion and sodium ion. , At least one cation selected from the group consisting of potassium ion and ammonium ion.

In the polymer compound for coating, when the monomer composition contains a salt (a13) of an anionic monomer, the content of the salt (a13) of the anionic monomer contained in the monomer composition is From the viewpoint of conductivity and adhesiveness, preferably 0.1 to 10% by weight, more preferably 0.5 to 5%, based on the total weight of the ester compound (a11) and the anionic monomer (a12). By weight%.

The weight average molecular weight (Mw) of the polymer compound for coating is preferably 20,000 to 300,000, more preferably 40,000 to 200,000 from the viewpoint of the balance between the adhesiveness with the active material and the coating rate. is there.
The weight average molecular weight (Mw) and the number average molecular weight (Mn) are measured by gel permeation chromatography (hereinafter abbreviated as GPC) measured under the following conditions.

<GPC measurement conditions>
-Device: Alliance GPC V2000 (manufactured by Waters)
-Solvent: Ortodichlorobenzene-Standard substance: Polystyrene-Sample concentration: 3 mg / ml
-Column stationary phase: PLgel 10 μm, two MIXED-B in series (manufactured by Polymer Laboratories)
-Column temperature: 135 ° C

The above-mentioned monomer composition includes a copolymerizable vinyl monomer (c) containing no active hydrogen in addition to the ester compound (a11), the anionic monomer (a12) and the salt of the anionic monomer (a13). ) [Hereinafter referred to as copolymerizable vinyl monomer (c)] and at least one of the cross-linking agent (d) may be contained.

Examples of the copolymerizable vinyl monomer (c) include the following (c1) to (c5).

(C1) Formed from branched or linear aliphatic monools having 13 to 20 carbon atoms, alicyclic monools having 5 to 20 carbon atoms or aromatic aliphatic monools having 7 to 20 carbon atoms and (meth) acrylic acid. The above-mentioned monools include (i) branched or linear aliphatic monools having 13 to 20 carbon atoms (tridecyl alcohol, tetradecyl alcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearyl alcohol, iso). Stearyl alcohol, nonadecil alcohol, arachidyl alcohol, etc.), (ii) alicyclic monool with 5 to 20 carbon atoms (cyclohexyl alcohol, etc.), (iii) aromatic aliphatic monool with 7 to 20 carbon atoms (benzyl alcohol, etc.) Etc.) and a mixture of two or more of these.

(C2) Poly (n = 2 to 30) Oxyalkylene (2 to 4 carbon atoms) Alkyl (1 to 18 carbon atoms) Ether (meth) Acrylate [Methanol ethylene oxide (hereinafter abbreviated as EO) 10 mol adduct and (meth) ) Ester compound with acrylic acid and propylene oxide of methanol (hereinafter abbreviated as PO) 10 mol adduct and (meth) acrylic acid ester compound, etc.].

(C3) Nitrogen-containing vinyl compound (c3-1) Amide group-containing vinyl compound (i) (Meta) acrylamide compound having 3 to 30 carbon atoms, such as N, N-dialkyl (1 to 6 carbon atoms) or dialalkyl (carbon number) 7 to 15) (meth) acrylamide (N, N-dimethylacrylamide, N, N-dibenzylacrylamide, etc.) and diacetone acrylamide.
(Ii) Excluding the above (meth) acrylamide compound, an amide group-containing vinyl compound having 4 to 20 carbon atoms, for example, N-methyl-N-vinylacetamide, cyclic amide [pyrrolidone compound having 6 to 13 carbon atoms (N-vinylpyrrolidone) etc)].

(C3-2) (Meta) Acrylate Compound (i) Dialkyl (1 to 4 Carbons) Aminoalkyl (1 to 4 Carbons) (Meta) Acrylate [N, N-Dimethylaminoethyl (Meta) Acrylate, N, N -Diethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, morpholinoethyl (meth) acrylate, etc.].
(Ii) Haloalkane quaternary ammonium group-containing (meth) acrylate {tertiary amino group-containing (meth) acrylate [N, N-dimethylaminoethyl (meth) acrylate and N, N-diethylaminoethyl (meth) acrylate, etc.] A quaternary product, etc. quaternized with a quaternary agent such as alkyl}.

(C3-3) Heterocycle-containing vinyl compound A pyridine compound having 7 to 14 carbon atoms (2- or 4-vinylpyridine, etc.), an imidazole compound having 5 to 12 carbon atoms (N-vinylimidazole, etc.), 6 to 13 carbon atoms. Pyrrole compound (N-vinylpyrrole etc.) and pyrrolidone compound having 6 to 13 carbon atoms (N-vinyl-2-pyrrolidone etc.).

(C3-4) Nitrile Group-Containing Vinyl Compound A nitrile group-containing vinyl compound having 3 to 15 carbon atoms [(meth) acrylonitrile, cyanostyrene, alkyl (1 to 4 carbon atoms) cyanoacrylate, etc.].

(C3-5) Other Vinyl Compounds Nitro group-containing vinyl compounds having 8 to 16 carbon atoms (nitrostyrene, etc.) and the like.

(C4) Vinyl Hydrocarbons (c4-1) aliphatic Vinyl Hydrocarbons Olefins having 2 to 18 or more carbon atoms (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.), Dienes having 4 to 10 or more carbon atoms (butadiene, isobutylene, 1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene, etc.) and the like.

(C4-2) Alicyclic vinyl hydrocarbons Cyclic unsaturated compounds with 4 to 18 or more carbon atoms [cycloalkene (cyclohexene, vinylcyclohexene, indene, etc.), cycloalkane (cyclopentadiene, etc.), bicycloalkene (ethylidene, etc.) Bicyclohexene, etc.), Bicycloalkadiene (dicyclopentadiene, etc.) and terpenes (pinene, limonene, etc.)], etc.

(C4-3) Aromatic Vinyl Hydrocarbons Aromatic unsaturated compounds having 8 to 20 or more carbon atoms and their derivatives (styrene, α-methylstyrene, vinyltorene, 2,4-dimethylstyrene, ethylstyrene, isopropyl) Styrene, butyl styrene, phenyl styrene, cyclohexyl styrene, benzyl styrene, etc.), etc.

(C5) Vinyl Group-Containing Ester Compound, Vinyl Group-Containing Ether Compound, Vinyl Ketone and Unsaturated Dicarboxylic Acid Diester (c5-1) Vinyl Group-Containing Ester Compound Aliper Vinyl Ester Or an alkenyl ester of (dicarboxylic acid) (vinyl acetate, vinyl propionate, vinyl butyrate, diallyl adipate, isopropenyl acetate, methoxyvinyl acetate, etc.)].
Aromatic vinyl esters [Aromatic ester of aromatic carboxylic acid (mono- or dicarboxylic acid) having 9 to 20 carbon atoms (vinyl benzoate, methyl 4-vinyl benzoate, etc.) and aromatic ring-containing ester of aliphatic carboxylic acid (acetoxystyrene) And so on].

(C5-2) Vinyl group-containing ether compound aliphatic vinyl ether [vinyl alkyl (carbon number 1 to 10) ether (vinyl methyl ether, vinyl butyl ether, vinyl 2-ethylhexyl ether, etc.) having 3 to 15 carbon atoms, vinyl alkoxy (carbon) Numbers 1-6) Alkyl (1 to 4 carbon atoms) ethers (vinyl-2-methoxyethyl ether, methoxybutadiene, 3,4-dihydro-1,2-pyran, 2-butoxy-2'-vinyloxydiethyl ether and Vinyl-2-ethyl mercaptoethyl ether, etc.), Poly (2-4) (meth) allyloxyalkanes (2-6 carbon atoms) (dialyloxyethane, trialiloxietan, tetraaryroxybutane and tetramethalyloxy) Ether, etc.)].
Aromatic vinyl ether having 8 to 20 carbon atoms (vinyl phenyl ether, phenoxystyrene, etc.).

(C5-3) Vinyl Ketone An aliphatic vinyl ketone having 4 to 25 carbon atoms (vinyl methyl ketone, vinyl ethyl ketone, etc.), an aromatic vinyl ketone having 9 to 21 carbon atoms (vinyl phenyl ketone, etc.) and the like.

(C5-4) Unsaturated dicarboxylic acid diester Unsaturated dicarboxylic acid diester having 4 to 34 carbon atoms [Dialkyl fumarate (two alkyl groups are linear, branched or alicyclic with 1 to 22 carbon atoms). (Groups) and dialkylmalates (two alkyl groups are linear, branched or alicyclic groups having 1 to 22 carbon atoms), etc.].

When the above-mentioned monomer composition contains a copolymerizable vinyl monomer (c), the content of the copolymerizable vinyl monomer (c) is the total weight of the ester compound (a11) and the anionic monomer (a12). It is preferably 10 to 50% by weight based on.

<Crosslinking agent (d)>
Examples of the cross-linking agent (d) include a monomer having two vinyl groups (d2) and a monomer having three or more vinyl groups (d3).
Examples of the monomer (d2) include di (meth) acrylates of diols having 2 to 12 carbon atoms, specifically, ethylene glycol di (meth) acrylates, 1,4-butanediol di (meth) acrylates, and 1 , 6-Hexanediol di (meth) acrylate, dodecanediol di (meth) acrylate.
Examples of the monomer (d3) include trimethylolpropane tri (meth) acrylate and pentaerythritol tetra (meth) acrylate.
Among the cross-linking agents (d), (d2) is preferable from the viewpoint of molecular weight adjustment and adhesiveness.

When the monomer composition contains the cross-linking agent (d), the weight of the cross-linking agent (d) is adjusted in molecular weight and adhesiveness based on the weight of all the monomers constituting the coating polymer compound. From the viewpoint of the above, it is preferably 0.05 to 2.5% by weight, more preferably 0.1 to 1% by weight.

The glass transition point of the polymer compound for coating [hereinafter abbreviated as Tg, measuring method: DSC (scanning differential thermal analysis) method] is preferably 50 to 200 ° C., more preferably 70 to 70 to 200 ° C. from the viewpoint of battery heat resistance. The temperature is 180 ° C., particularly preferably 80 to 150 ° C., and can be appropriately adjusted depending on the type and weight of each monomer.

The coating polymer compound can be obtained by polymerizing the above-mentioned monomer composition, and a known polymerization method (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.) is used as the polymerization method. Can be done.
In the polymerization, known polymerization initiators {azo-based initiators [2,2'-azobis (2-methylpropionitrile), 2,2'-azobis (2,4-dimethylvaleronitrile) and 2,2' -Azobis (2-methylbutyronitrile), etc.], a peroxide-based initiator (benzoyl peroxide, di-t-butyl peroxide, lauryl peroxide, etc.), etc.} can be used.
The amount of the polymerization initiator used is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, based on the total weight of the monomer components contained in the monomer composition.

Examples of the solvent used in the case of solution polymerization include an ester solvent [preferably an ester compound having 2 to 8 carbon atoms (for example, ethyl acetate and butyl acetate)], and an alcohol [preferably an aliphatic alcohol having 1 to 8 carbon atoms (for example,). Methanol, ethanol, isopropanol and octanol)], hydrocarbons with linear, branched or cyclic structures with 5-8 carbon atoms (eg pentane, hexane, heptane, octane, cyclohexane, toluene and xylene), amide solvents [eg N, Examples thereof include N-dimethylformamide (hereinafter abbreviated as DMF) and dimethylacetamide] and a ketone solvent [preferably a ketone compound having 3 to 9 carbon atoms (for example, methyl ethyl ketone)].
The amount of the solvent used is, for example, 50 to 200% by weight based on the total weight of the monomer components contained in the monomer composition, and the concentration of the monomer composition in the reaction solution is, for example, 30 to 200% by weight. It is 70% by weight.

The in-system temperature in the polymerization reaction is usually −5 to 150 ° C., preferably 30 to 120 ° C., the reaction time is usually 0.1 to 50 hours, preferably 2 to 24 hours, and the end point of the polymerization reaction has not yet been reached. The amount of the reaction monomer is usually 5% by weight or less, preferably 1% by weight or less, based on the total weight of the monomer components contained in the monomer composition. The amount can be confirmed by a known method for quantifying the monomer content such as gas chromatography.

<Conducting agent>
The conductive agent contained in the coating layer is selected from materials having conductivity.
Specifically, metals [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.] and carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.), etc.), etc. ], Etc. can be mentioned.
These conductive agents may be used alone or in combination of two or more, but are not limited thereto.
Moreover, you may use these alloys or metal oxides. From the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, copper, titanium and mixtures thereof are preferable, silver, aluminum, stainless steel and carbon are more preferable, and carbon is even more preferable. Further, these conductive agents may be those obtained by coating a conductive material (a metal material among the above-mentioned conductive agent materials) around a particle-based ceramic material or a resin material by plating or the like.

The average particle size of the conductive agent is not particularly limited, but is preferably 0.01 to 10 μm, more preferably 0.02 to 5 μm, and 0. It is more preferably 03 to 1 μm.
In the present specification, the "particle size" of the conductive agent means the maximum distance L among the distances between any two points on the contour line of the conductive agent. As the value of the "average particle size" of the conductive agent, the particle size of the particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value shall be adopted.

The shape (form) of the conductive agent is not limited to the particle form, and may be a form other than the particle form, or may be a form practically used as a so-called filler-based conductive resin composition such as carbon nanotubes. ..

The conductive agent may be a conductive fiber whose shape is fibrous.
Conductive fibers include polyacrylonitrile (PAN) -based carbon fibers, pitch-based carbon fibers and other carbon fibers, conductive fibers in which highly conductive metals and graphite are uniformly dispersed in synthetic fibers, and stainless steel. Metal fibers made from such metals, conductive fibers whose surface is coated with metal, conductive fibers whose surface is coated with a resin containing a conductive substance, polypropylene resin kneaded with graphene, etc. Can be mentioned. Among these conductive fibers, polypropylene resin kneaded with carbon fibers and graphene is preferable from the viewpoint of price, electrochemical stability and the like.
When the conductive agent is a conductive fiber, the average fiber diameter thereof is preferably 0.1 to 20 μm from the viewpoint of conductivity, mechanical strength and dispersibility.

<Coated positive electrode active material for lithium-ion batteries (P)>
In the coated positive electrode active material (P) for a lithium ion battery of the present invention, at least a part of the surface of the positive electrode active material for a lithium ion battery is coated with a coating layer containing a coating polymer compound and a conductive agent. It is a coated positive electrode active material for a lithium ion battery, and has a covering ratio of 65 to 96% as measured by X-ray photoelectron spectroscopy (XPS).
The coverage is preferably 70 to 93%, more preferably 75 to 90% from the viewpoint of cycle characteristics.

When measuring the coverage, XPS measurement of the coated positive electrode active material (P) is performed using "PHI5800 ESCA SYSTEM" manufactured by ULVAC-PHI.
For example, when the positive electrode active material is LiNi _0.86 Co _0.06 Al _0.02 Mn _0.06 O ₂ , each spectrum type has C (carbon) in the 1s orbital, Co in the 2p orbital, and Al in the Al. 2p orbital, Mn is 2p orbital, Ni is 2p orbital, and it is calculated by the following formula from the integrated value of each spectrum.
Coverage (%) = "C" x 100 / ("C" + "Ni" + "Co" + "Al" + "Mn")

The ratio of the total weight of the polymer compound and the conductive agent to the weight of the positive electrode active material for the lithium ion battery is preferably 2 to 25% by weight.

The ratio of the weight of the polymer compound to the weight of the coated positive electrode active material for a lithium ion battery is preferably 0.1 to 11% by weight, more preferably 1 to 5% by weight.
The ratio of the weight of the conductive agent to the weight of the coated positive electrode active material for a lithium ion battery is preferably 2 to 14% by weight, more preferably 2 to 10% by weight.

The conductivity of the coating layer is preferably 0.001 to 10 mS / cm, more preferably 0.01 to 5 mS / cm.
The conductivity of the coating layer can be determined by the four-terminal method.
When the conductivity of the coating layer is 0.001 mS / cm or more, the internal resistance of the lithium ion battery does not become too high, which is preferable.

The coated positive electrode active material (P) for a lithium ion battery of the present invention can be produced, for example, by the following production method.
(1) The polymer compound, the conductive agent, and the positive electrode active material for a lithium ion battery are mixed.
(2) After preparing a coating material by mixing a polymer compound and a conductive agent, the coating material and a positive electrode active material for a lithium ion battery are mixed.
(3) A solution containing a polymer compound and a solvent and a positive electrode active material for a lithium ion battery are mixed, then a conductive agent is mixed, and the solvent is distilled off if necessary.
(4) After mixing a mixed solution containing a polymer compound, a conductive agent and a solvent, and a positive electrode active material for a lithium ion battery, the solvent is distilled off if necessary.

In order to keep the coverage in the present invention within a preferable range, it is preferable to mix a positive electrode active material for a lithium ion battery, a polymer compound, a conductive agent, and a solvent. Therefore, among the above (1) to (4), (3) or (4) is preferable, and (3) is more preferable, from the viewpoint of setting the coverage within a preferable range.

In the production method of (3) or (4) above, examples of the solvent include N, N-dimethylformamide (DMF), toluene, xylene and acetone.
Of these, from the viewpoint of cycle characteristics, toluene, xylene and acetone are preferable, and toluene and xylene are more preferable.
Further, in the above (3) or (4), the weight ratio of the polymer compound to the solvent [(polymer compound) / (solvent)] is preferably 10/90 to 40 from the viewpoint of a preferable range of the coverage. / 60, more preferably 20/80 to 35/65, and particularly preferably 25/75 to 30/70.

In order to keep the coverage in the present invention within a preferable range, for example, the following method can be used.
(1) Set the positive electrode active material for the lithium ion battery, the polymer compound, and the conductive agent to preferable ones and preferable weight ratios, respectively.
(2) In the above-mentioned production methods (1) to (4), a preferable production method is adopted.
(3) In the above production methods (3) and (4), in order to control the interface state between the positive electrode active material and the polymer compound, the absolute difference between the surface free energy of the positive electrode active material and the surface free energy of the solvent is absolute. The value (ΔE, unit: mN / m) is preferably set to 10 to 30, more preferably 15 to 25.

In the present invention, the surface free energy of the positive electrode active material is obtained by using a powder wet permeation analyzer [“PW-500”, manufactured by Kyowa Interface Science Co., Ltd.] with a solvent known by the permeation rate method and a powder sample. The contact angle is measured, and the value of the contact angle is used in the Owns-Wendt method (“Journal of Applied Polymer Science, August, 1969, Volume 13, Issue 8, P1741-1747” and “Surface, 2005, Volume 43, Volume 43”. It is a value calculated by the method described in ~ 318 ”).
In addition, surface free energy and surface tension are quantities that have equivalent dimensions as physical quantities, and if they are expressed in the same unit system, the numerical values will be the same. The surface free energy of the solvent (= surface tension of the solvent) in the present invention is a value calculated by the pendant drop method using a pendant drop type surface tension measuring device [“PW-D”, manufactured by Kyowa Interface Science Co., Ltd.]. is there.

When the coated positive electrode active material for a lithium ion battery of the present invention is used as a positive electrode, the coated positive electrode active material for a lithium ion battery and the conductive material are dispersed at a concentration of 30 to 60% by weight based on the weight of the dispersion liquid to form a slurry. After applying the converted dispersion to the current collector with a coating device such as a bar coater, it is dried when water or a solvent is used as the dispersion medium, and is excessive when an electrolytic solution is used as the dispersion medium. The dispersion medium may be removed by absorbing the electrolytic solution of the above by an absorber such as a sponge or by sucking it through a mesh, and if necessary, pressing with a press machine may be performed.

If necessary, a known electrode binder [polyvinylidene fluoride (PVdF), etc.] contained in a known positive electrode for a lithium ion battery may be added to the dispersion liquid, but no electrode binder is added. Is preferable. In a conventionally known positive electrode for a lithium ion battery that does not use a coated positive electrode active material as the positive electrode active material, it is necessary to maintain the conductive path by fixing the positive electrode active material in the positive electrode with an electrode binder. However, when the coated positive electrode active material for a lithium ion battery of the present invention is used, the conductive path can be maintained without fixing the positive electrode active material in the positive electrode by the action of the coating layer, so an electrode binder is added. You don't have to. By not adding the binder for the electrode, the positive electrode active material is not immobilized in the positive electrode, so that the ability to alleviate the volume change of the positive electrode active material is further improved.

The conductive material used for manufacturing the electrode is different from the conductive agent contained in the coating layer, exists outside the coating layer of the coated positive electrode active material, and has electrons from the surface of the coated positive electrode active material in the active material layer. It has a function to improve conductivity.

Among the dispersion media, examples of water include ion-exchanged water and ultrapure water.
Among the dispersion media, as the electrolytic solution, the same electrolytic solution (described later) used when producing a lithium ion battery using the positive electrode containing the coated positive electrode active material for the lithium ion battery of the present invention may be used. it can.
Among the dispersion media, the solvent used is the same as the non-aqueous solvent constituting the electrolytic solution used when producing a lithium ion battery using the positive electrode containing the coated positive electrode active material for the lithium ion battery of the present invention. In addition to these, 1-methyl-2-pyrrolidone, dimethylacetamide, N, N-dimethylaminopropylamine and the like can be mentioned.

Examples of the current collector include a metal foil such as copper, aluminum, titanium, stainless steel and nickel, a resin current collector made of a conductive polymer (described in Japanese Patent Application Laid-Open No. 2012-150905, etc.), and conductive carbon. Examples include sheets and conductive glass sheets.

Examples of the binder for the electrode include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene and polypropylene.

As the conductive material used together with the coated positive electrode active material for the lithium ion battery in the manufacture of the electrode, the same conductive material as that contained in the coating layer can be used.

When producing a lithium ion battery using a positive electrode containing a coated positive electrode active material for a lithium ion battery of the present invention, the electrodes to be opposite electrodes are combined, housed in a cell container together with a separator, and an electrolytic solution is injected into the cell. It can be manufactured by a method of sealing the container or the like.
Further, a positive electrode is formed on one surface of the current collector and a negative electrode is formed on the other surface to prepare a bipolar electrode, and the bipolar electrode is laminated with a separator and stored in a cell container to store an electrolytic solution. It can also be obtained by injecting and sealing the cell container.

Examples of the separator include a microporous film made of polyethylene film or polypropylene film, a multilayer film of a porous polyethylene film and polypropylene, a non-woven fabric made of polyester fiber, aramid fiber, glass fiber, etc., and silica and alumina on their surfaces. , Known separators for lithium ion batteries such as those to which ceramic fine particles such as titania are attached can be mentioned.

As the electrolytic solution to be injected into the cell container, a known electrolytic solution containing an electrolyte and a non-aqueous solvent, which is used in the production of a known lithium ion battery, can be used.

As the electrolyte, can be used such as those used in the known electrolytic solution, the lithium salt of an inorganic acid _{(LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6 , and LiClO _4, etc.) and a lithium salt of an organic acid {LiN ( CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _2, LiC (CF ₃ SO ₂ ) _3, etc.} and the like can be mentioned. _{Of these, LiPF 6} is preferable from the viewpoint of battery output and charge / discharge cycle characteristics.

As the non-aqueous solvent, those used in known electrolytic solutions can be used, and for example, a lactone compound, a cyclic or chain carbonate, a chain carboxylic acid ester, a cyclic or chain ether, a phosphoric acid ester, or a nitrile can be used. Compounds, amide compounds, sulfones, sulfolanes and mixtures thereof can be used.

Examples of the lactone compound include a 5-membered ring (γ-butyrolactone, γ-valerolactone, etc.) and a 6-membered ring lactone compound (δ-valerolactone, etc.).

Examples of the cyclic carbonate include propylene carbonate, ethylene carbonate and butylene carbonate.
Examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, di-n-propyl carbonate and the like.

Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, methyl propionate and the like.
Examples of the cyclic ether include tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 1,4-dioxane and the like.
Examples of the chain ether include dimethoxymethane and 1,2-dimethoxyethane.

Phosphate esters include trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, tripropyl phosphate, tributyl phosphate, tri (trifluoromethyl) phosphate, tri (trichloromethyl) phosphate, Tri (trifluoroethyl) phosphate, tri (triperfluoroethyl) phosphate, 2-ethoxy-1,3,2-dioxaphosphoran-2-one, 2-trifluoroethoxy-1,3,2- Examples thereof include dioxaphosphoran-2-one and 2-methoxyethoxy-1,3,2-dioxaphosphoran-2-one.
Examples of the nitrile compound include acetonitrile and the like. Examples of the amide compound include DMF and the like. Examples of the sulfone include dimethyl sulfone and diethyl sulfone.
One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

Among the non-aqueous solvents, lactone compounds, cyclic carbonates, chain carbonates and phosphate esters are preferable from the viewpoint of battery output and charge / discharge cycle characteristics, and lactone compounds, cyclic carbonates and chains are more preferable. A carbonic acid ester is particularly preferable, and a mixed solution of a cyclic carbonic acid ester and a chain carbonic acid ester is particularly preferable. The most preferable is a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC), or a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC).

The lithium ion battery produced by using the coated positive electrode active material for the lithium ion battery of the present invention has high reliability at the time of abnormality. The details of the mechanism are not clear, but it can be estimated as follows.
The temperature rises when the charged positive electrode particles and the negative electrode particles come into contact with each other. At that time, the electrolyte solvent contained in the resin is gasified. Due to the positive pressure during gasification
(1) The positive and negative electrode particles that are in contact with each other are separated.
(2) The conductive auxiliary agent in the resin exhibits conductivity by the structure structure, and the structure structure is cut by the positive pressure at the time of gasification.
By (1) and (2), the conductivity is lost to prevent a local current from flowing, and the temperature rise inside the battery is suppressed.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Hereinafter, unless otherwise specified,% indicates a weight% and a part indicates a weight part.

<Manufacturing example 1>
70.0 parts of toluene was charged into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel and a nitrogen gas introduction tube, and the temperature was raised to 75 ° C. Next, a solution obtained by mixing a monomer composition (95.0 parts of dodecyl methacrylate, 4.6 parts of methacrylic acid and 0.4 part of 1,6-hexanediol dimethacrylate) and 20 parts of DMF, and 2,2'-. A solution of 0.8 parts of azobis (2-methylbutyronitrile) dissolved in 10.0 parts of DMF was continuously blown into a four-necked flask while stirring with a dropping funnel over 2 hours. Radical polymerization was carried out by dropping. After completion of the dropping, the reaction was continued at 75 ° C. for 3 hours. Then, the temperature was raised to 80 ° C. and the reaction was continued for 3 hours to obtain a copolymer solution having a resin concentration of 50%. The obtained copolymer solution was transferred to a Teflon (registered trademark) vat and dried under reduced pressure at 120 ° C. and 0.01 MPa for 3 hours to distill off toluene and DMF to obtain a copolymer. This copolymer was roughly pulverized with a hammer and then additionally pulverized in a mortar to obtain a coating polymer compound (R-1).
The acid value of (R-1) was 30 mgKOH / g, and the weight average molecular weight (Mw) was 90,000.

<Acid value measurement conditions>
・ Equipment: Automatic titrator COM-1700 (manufactured by Hiranuma Sangyo Co., Ltd.)
The measurement was performed using an automatic titrator [COM-1700 (manufactured by Hiranuma Sangyo Co., Ltd.)] according to the potentiometric titration method described in JIS K 0070-1922.

<GPC measurement conditions>
-Device: Alliance GPC V2000 (manufactured by Waters)
-Solvent: orthodichlorobenzene, DMF, THF
-Standard substance: Polystyrene-Sample concentration: 3 mg / ml
-Column stationary phase: PLgel 10 μm, MIXED-B 2 in series (manufactured by Polymer Laboratories)
-Column temperature: 135 ° C

<Manufacturing Examples 2-5>
Same as Production Example 1 except that the ester compound (a11), anionic monomer (a12), copolymerizable vinyl monomer (c), and cross-linking agent (d) shown in Table 1 were used in Production Example 1. Then, the coating polymer compounds (R-2) to (R-5) were obtained.
Table 1 shows the acid value and weight average molecular weight of the coating polymer compounds (R-2) to (R-5).

<Example 1>
[Preparation of coated positive electrode active material]
100 parts of positive electrode active material powder (LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder, volume average particle diameter 4 μm) was placed in a universal mixer high-speed mixer FS25 [manufactured by Artecnica Co., Ltd.] at room temperature. With stirring at 720 rpm, 12.0 parts of the coating polymer compound solution (25% by weight solution) obtained by dissolving the coating polymer compound (R-1) in toluene was added dropwise over 2 minutes. The mixture was further stirred for 5 minutes.
Then, in a stirred state, 3.0 parts of acetylene black [Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd.] was added as a conductive agent in 2 minutes while being divided, and stirring was continued for 30 minutes. Then, the pressure was reduced to 0.01 MPa while maintaining the stirring, then the temperature was raised to 140 ° C. while maintaining the stirring and the degree of pressure reduction, and the stirring, the degree of pressure reduction and the temperature were maintained for 8 hours to distill off the volatile matter. .. The obtained powder was classified with a sieve having an opening of 106 μm to obtain a coated positive electrode active material (P-1). The coverage of the coated positive electrode active material (P-1) by XPS was 82%.

<Examples 2 to 13, Comparative Examples 1 to 2>
In Example 1, the coated positive electrode active materials (P-2) to (P) are the same as in Example 1 except that the positive electrode active material powder, the polymer compound solution for coating, and the conductive agent shown in Table 2 are used. -13), (P'-1) to (P'-2) were obtained. The coverage of each coated positive electrode active material by XPS was measured.

For each of the obtained coated positive electrode active materials (P), a lithium ion battery for evaluation of the positive electrode was prepared by the procedure described later, and the 50 cycle (cyc) capacity retention rate of the lithium ion battery was measured.
The results are shown in Table 2. In Table 2, "DMSO" is dimethyl sulfoxide.

[Manufacturing of lithium-ion battery for positive electrode evaluation]
42 parts of electrolyte for lithium ion battery and carbon fiber [Osaka Gas] prepared by dissolving _{LiPF 6} in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and diethyl carbonate (DEC) at a ratio of 1 mol / L. Donna Carbo Mild S-243 manufactured by Chemical Co., Ltd .: Average fiber length 500 μm, average fiber diameter 13 μm: electrical conductivity 200 mS / cm] 4.2 parts and planetary stirring type mixing and kneading device {Awatori Kentarou [Co., Ltd.] Using [Shinky]}, the mixture was mixed at 2000 rpm for 7 minutes, and then 30 parts of the above electrolytic solution and 206 parts of the obtained coated positive electrode active material (P) were added, and then by Rentaro Awatori at 2000 rpm. Mix for 5 minutes, add 20 parts of the electrolyte, and then stir with Awatori Kentarou at 2000 rpm for 1 minute. After adding 2.3 parts of the electrolyte, stir with Awatori Kentarou at 2000 rpm. Was mixed for 1.5 minutes to prepare a positive electrode active material slurry.
Each of the obtained positive electrode active material slurries is applied to one side of a carbon-coated aluminum foil having a thickness of 50 μm, pressed at a pressure of 10 MPa for about 10 seconds, and has a thickness of about 400 μm for an evaluation lithium ion battery positive electrode (3 cm × 3 cm). ) Was prepared.
Carbon-coated aluminum foil (3 cm x 3 cm) with terminals (5 mm x 3 cm), one separator (made of Cellguard 2500 PP) (5 cm x 5 cm), and copper foil with terminals (5 mm x 3 cm) (3 cm x 3 cm) in the same direction Two terminals are laminated in order in the direction in which they come out, sandwiched between two commercially available heat-sealing aluminum laminate films (8 cm x 8 cm), and one side where the terminals come out is heat-sealed for positive electrode evaluation. A laminated cell was prepared.
Next, between the carbon-coated aluminum foil and the separator, the positive electrode for evaluation lithium-ion battery (3 cm × 3 cm) obtained above was placed between the carbon-coated aluminum foil of the laminated cell and the carbon-coated aluminum foil of the positive electrode for the lithium-ion battery. It was inserted in a contacting direction, and 70 μL of an electrolytic solution was further injected onto the electrode to allow the electrode to absorb the electrolytic solution. Next, 70 μL of the electrolytic solution was injected onto the separator.
Then, a lithium foil was inserted between the separator and the copper foil, and the two sides orthogonal to the first heat-sealed side were heat-sealed.
Then, 70 μL of an electrolytic solution was further injected from the opening, and the laminated cell was sealed by heat-sealing the opening while evacuating the inside of the cell using a vacuum sealer to obtain a lithium ion battery for positive electrode evaluation.

<Measurement of 50 cyc capacity retention rate of lithium-ion battery, evaluation of cycle characteristics>
The obtained lithium ion battery for positive electrode evaluation was evaluated by the following method using a charge / discharge measuring device "HJ-SD8" [manufactured by Hokuto Denko Co., Ltd.] at 45 ° C.
It was charged to 4.2 V with a current of 0.1 C by a constant current constant voltage charging method (also referred to as CCCV mode), and after a 10-minute rest, it was discharged to 2.6 V with a current of 0.1 C. This charging / discharging was repeated up to 50 cycles (50 cycls).
From the discharge capacity of the 1st cyc and the discharge capacity of the 50th cyc, the capacity retention rate was calculated by the following formula.
[50 cyc capacity retention rate (%)] =
[50th cyc discharge capacity] x 100 / [1st cyc discharge capacity]

From the results of Tables 1 and 2, the coated positive electrode active materials (P-1) to (P-13) of Examples 1 to 13 are the coated positive electrode active materials (P'-1) to (P'-1) to Comparative Examples 1 and 2. It can be seen that a lithium ion battery having an excellent capacity retention rate and excellent cycle characteristics is provided as compared with P'-2).

The coated positive electrode active material for lithium ion batteries of the present invention is particularly useful as a positive electrode active material for bipolar secondary batteries and lithium ion secondary batteries used for mobile phones, personal computers, hybrid vehicles and electric vehicles. Is.

Claims (4)

A coated positive electrode active material for a lithium ion battery, wherein at least a part of the surface of the positive electrode active material for a lithium ion battery is coated with a coating layer containing a polymer compound for coating and a conductive agent.
A coated positive electrode active material (P) for a lithium ion battery having a coverage of 65 to 96% as measured by X-ray photoelectron spectroscopy. A monomer composition in which the coating polymer compound contains an ester compound (a11) of a monovalent aliphatic alcohol having 1 to 12 carbon atoms and (meth) acrylic acid and an anionic monomer (a12). The coated positive electrode active material for a lithium ion battery according to claim 1, which is a polymer of a compound and has an acid value of 5 to 200 mgKOH / g. The anionic monomer (a12) contains a radically polymerizable unsaturated carboxylic acid having 3 to 9 carbon atoms, a radically polymerizable unsaturated sulfonic acid having 2 to 8 carbon atoms, and a radically polymerizable unsaturated sulfonic acid having 2 to 9 carbon atoms. The coated positive electrode active material for a lithium ion battery according to claim 2, which is at least one selected from the group consisting of phosphonic acid. The method for producing a coated positive electrode active material for a lithium ion battery according to any one of claims 1 to 3.
It has a step of mixing a positive electrode active material for a lithium ion battery, a polymer compound for coating, a conductive agent, and a solvent.
A method for producing a coated positive electrode active material for a lithium ion battery, wherein the absolute value (ΔE) of the difference between the surface free energy of the positive electrode active material for a lithium ion battery and the surface free energy of the solvent is 10 to 30 mN / m.